Based on recent 20-year inspections of steel tanks used to store corrosive fuel products, tank owners are achieving at least 20-year service lives from single-coat epoxies used to line the tanks and protect them from corrosion. Those linings are being certified for another 10-year inspection cycle. This development shows promise that the industry has found a new minimum 30-year liner after switching from the difficult, hazardous and expensive-to-install vinyl ester systems that once dominated the market.

In 1998, a new 116,000-bbl aboveground steel storage tank owned by a U.S. refining and chemicals company was one of the first tanks to use the then-emerging single-coat epoxy coating. The coating was more applicator-friendly and faster to install than vinyl ester laminates, but only time would tell if it could achieve the same 30-year service life that was possible from vinyl ester systems.

After the tank held corrosive fuel products for 20 years, inspectors found a fully intact lining showing no signs of failure. They were able to recertify the lining for another 10 years, showing potential that a minimum 30-year service life is possible.

‘Swing Service’ Requirements
The tank was built to store various fuel products for distribution, including diesel fuel, unleaded gasoline and kerosene. Due to this “swing service” requirement, the lining needed to meet or exceed the rigors of holding the most corrosive contents that could be stored inside the tank. The lining would therefore require sufficient chemical resistance, as well as ample flexibility and edge-retention properties to handle expansion and contraction of the tank.

The owner chose the then new-to-market Dura-Plate UHS Epoxy lining system from Sherwin-Williams Protective & Marine Coatings. The lining was designed for long-term immersion service in oil tanks and refined fuel storage tanks. It combines broad chemical resistance with excellent flexibility (5%) and edge retention (greater than 75%). The high-build, ultra-high solids epoxy amine can also be applied in one coat—up to 50- to 60-mils dry film thickness (DFT).

To line the tank, applicators abrasive-blasted its interior floor and 3-ft shell surface to ensure the steel was free of rust and contaminants. Next, they spray-applied the Dura-Plate UHS Epoxy coating to the floor and shell, creating a monolithic lining with a 20- to 25-mil DFT in a single application.

20-Year Inspection
During the tank’s first 10-year inspection in 2008, inspectors visually inspected the floor and shell and performed adhesion testing on the floor. They observed no signs of lining failure and only had to make minor repairs to small areas of mechanical damage caused during the inspection.

During the 20-year inspection, inspectors again found only minor mechanical damage. Applicators repaired those areas by abrading the surfaces down to bare steel, feathering out the edges of the existing lining and reapplying the coating to the original surface profile and DFT requirements, just as they had done at the 10-year mark.

In approving the lining for another 10-year inspection period, inspectors noted that the tank’s weld seams—which are a typical first line of failure for linings—were still like new and that the lining had no blisters, undercutting of welds or other issues.

Sherwin-Williams has inspected hundreds of single-coat epoxy-lined fuel storage tanks at 10 years that have been approved for additional 10-year inspection periods. The tank lined in 1998 is the first one to be inspected at 20 years, and inspectors were able to confidently certify it for another 10 years. At that time, all parties involved will know if the 30-year life is possible.

Visit Sherwin-Williams at booth 5071.